It is worth noting that some famous FGs are excluded from the list. As an example, we discuss the prototype of this category, NGC 1132 [1]}, for which we were not able to find \(\Delta m_{12}\) . There are indeed information on the fainter galaxies [2]}, but not a clear computation of the magnitude gap. However, [2]}, claimed that the second brightest galaxy is NGC 1126, a spiral galaxy located at \(8.4\)  arcminutes or 230 kpc in projection. The virial radius of this group is estimated to be \(r_{200} \sim 800\)  kpc, thus this galaxy should be inside 0.5 \(r_{200}\) . The difference in the velocity space is \(\Delta v = 438\)  km s\(^{-1}\) , as obtained using the Nasa Extragalactic Database (NED), so the two galaxies can be part of the same group, although a precise dynamical study should be done to confirm the membership.
In [2]} NGC 1126 is described as “seven times faniter in B”. We check in the SDSS DR16 the magnitudes of both NGC 1132 and NGC 1126: the former has \(m_r = 12.20\) , the latter \(m_r = 14.01\) , leading to a \(\Delta m_{12} = 1.81\) , rejecting it as a genuine FG. However, as we already mentioned, an accurate study of the membership of NGC 1126 to the group of NGC 1132 should be done and errors in SDSS magnitudes can not be excluded (NGC 1126 is flagged with “unreliable photometry”, as many other bright galaxies, mainly due to an over estimation of the sky around bright objects).
Concluding, with this example we aim at demonstrating that also the definition of the most commonly-accepted FGs may be not rigorous, or may need deeper studies to include them in a sample of genuine FGs.
